Electronic and Magnetic Properties of MnP-Type Binary Compounds

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Campbell, Daniel James
Paglione, Johnpierre
The interactions between electrons, and the resulting impact on physical properties, are at the heart of present-day materials science. This thesis looks at this idea through the lens of several compounds from a single family: the MnP-type transition metal pnictides. FeAs and FeP show long range magnetic order with some similarities to the high temperature, unconventional iron-based superconductors. CoAs lies on the border of magnetism, with strong fluctuations but no stable ordered state. CoP, in contrast, shows no strong magnetic fluctuations but serves as a useful baseline in determining the origin (from composition, structure, or magnetic order) of behavior in the other materials. For this work, single crystals were grown with two different techniques: solvent flux and chemical vapor transport. In the case of FeAs the flux method resulted in the highest quality crystals yet produced. Extensive work was then performed on these samples at the University of Maryland and the National High Magnetic Field Laboratory. Quantum oscillations observed in high magnetic fields, in combination with density functional theory calculations, give insight into the Fermi surfaces of these materials. Large magnetoresistance in the phosphides, but not the arsenides, demonstrates differences in the choice of pnictogen atom that cannot be simply a product of electron count. Angle-dependent linear magnetoresistance in FeP is a sign of a possible Dirac dispersion and topological physics, as has been hinted at in other MnP-type materials. Ultimately, it is possible to examine results for all four compounds and draw conclusions on the role of each of the two elements in the formula, which can be extended to other members of this family.